Molecular basis and clonal evolution of myeloproliferative neoplasms

Genetic Background of Polycythemia Vera

Polycythemia vera belongs to myeloproliferative neoplasms, essentially by affecting the erythroblastic lineage. JAK2 alterations have emerged as major driver mutations triggering PV-phenotype with the V617F mutation detected in nearly 98% of cases. That’s why JAK2 targeting therapeutic strategies have rapidly emerged to counter the aggravation of the disease. Over decades of research, to go further in the understanding of the disease and its evolution, a wide panel of genetic alterations affecting multiple genes has been highlighted. These are mainly involved in alternative splicing, epigenetic, miRNA regulation, intracellular signaling, and transcription factors expression. If JAK2 mutation, irrespective of the nature of the alteration, is known to be a crucial event for the disease to initiate, additional mutations seem to be markers of progression and poor prognosis. These discoveries have helped to characterize the complex genomic landscape of PV, resulting in potentially new adapted therapeutic strategies for patients concerning all the genetic interferences.

Role of tyrosine-kinase inhibitors in myeloproliferative neoplasms: comparative lessons learned

An important pathogenetic distinction in the classification of myeloproliferative neoplasms (MPNs) is the presence or absence of the BCR–ABL fusion gene, which encodes a unique oncogenic tyrosine kinase. The BCR–ABL fusion, caused by the formation of the Philadelphia chromosome (Ph) through translocation, constitutes the disease-initiating event in chronic myeloid leukemia. The development of successive BCR–ABL-targeted tyrosine-kinase inhibitors has led to greatly improved outcomes in patients with chronic myeloid leukemia, including high rates of complete hematologic, cytogenetic, and molecular responses. Such levels of treatment success have long been elusive for patients with Ph-negative MPNs, because of the difficulties in identifying specific driver proteins suitable as drug targets. However, in recent years an improved understanding of the complex pathobiology of classic Ph-negative MPNs, characterized by variable, overlapping multimutation profiles, has prompted the development of better and more broadly targeted (to pathway rather than protein) treatment options, particularly JAK inhibitors. In classic Ph-negative MPNs, overactivation of JAK-dependent signaling pathways is a central pathogenic mechanism, and mutually exclusive mutations in JAK2, MPL, and CALR linked to aberrant JAK activation are now recognized as key drivers of disease progression in myelofibrosis (MF). In clinical trials, the JAK1/JAK2 inhibitor ruxolitinib – the first therapy approved for MF worldwide – improved disease-related splenomegaly and symptoms independent of JAK2^V617F mutational status, and prolonged survival compared with placebo or standard therapy in patients with advanced MF. In separate trials, ruxolitinib also provided comprehensive hematologic control in patients with another Ph-negative MPN – polycythemia vera. However, complete cytogenetic or molecular responses with JAK inhibitors alone are normally not observed, underscoring the need for novel combination therapies of JAK inhibitors and complementary agents that better address the complexity of the pathobiology of classic Ph-negative MPNs. Here, we discuss the role of tyrosine-kinase inhibitors in the current MPN-treatment landscape.

The Role of MicroRNAs in Myeloproliferative Neoplasia

MiRs are 17-25 nucleotide non-coding RNAs. These RNAs target approximately 80% of protein coding mRNAs. MiRs control gene expression and altered expression of them affects the development of cancer. MiRs can function as tumor suppressor via down-regulation of proto-oncogenes and may function as oncogenes by suppressing tumor suppressors. Myeloproliferative neoplasias (formerly known as chronic myeloproliferative disorders) form a class of hematologic malignancies demonstrating the expansion of stem cells in one or more hematopoietic cell lines. CML results from an acquired translocation known as BCR-ABL (Philadelphia chromosome). JAK2V617F mutation is present in over 95% of PV, 55% of ET and 65% of PMF cases. Aberrant expression of miR is associated with myeloproliferative neoplasias, pathogenesis, disease progress and response to treatment. MiRs can also be potential therapeutic targets. CML is mainly treated by tyrosine kinase inhibitors such as Imatinib. In addition, altered function of miRs may be used as a prognostic factor in treatment. Resistance to Imatinib is currently a major clinical problem. The role of a number of miRs has been demonstrated in this resistance. Changing expression pattern of miRs can be effective in response to treatment and inhibition of drug resistance. In this paper, we set out to evaluate the effect of miRs in pathogenesis and treatment of MPN.

Leukemic transformation driven by an ASXL1 mutation after a JAK2V617F-positive primary myelofibrosis: clonal evolution and hierarchy revealed by next-generation sequencing

We have characterized the molecular changes underlying the transformation of a JAK2V617F⁺-myelofibrosis with trisomy 8, into a JAK2V617F-negative leukemia. Leukemic clone did not carry JAK2V617F mutation, but showed ASXL1 mutation (R693X). This mutation was identified in a low percentage at diagnosis by next-generation sequencing. Using this technology in serial specimens during the follow-up, we observed a progressive expansion of the ASXL1-mutated minor clone, whereas the JAK2V617F⁺-clone carrying trisomy 8 decreased. Hematologic progression occurred simultaneously with an ASXL1-R693X-negative lung-cancer. This is the first report showing a clear association between the expansion of an ASXL1-mutated clone and the leukemic transformation of myelofibrosis.

Outcome of patients with splanchnic venous thrombosis presenting without overt MPN: a role for the JAK2 V617F mutation re-evaluation

INTRODUCTION

Although investigation for JAK2 V617F mutation is recommended in patients presenting with splanchnic venous thrombosis (SVT), no specific clinical advice is given to SVT patients presenting without myeloproliferative neoplasms (MPN) and JAK2 V617F mutation. In MPN-free SVT patients, to investigate the clinical outcome, the clinical impact of re-evaluation for the JAK2 V617F mutation, and relationships with the occurrence and time to diagnosis of MPN.

MATERIALS AND METHODS

A cohort of non-cirrhotic SVT patients, enrolled at a single centre and prospectively analyzed.

RESULTS

In 121 SVT patients prospectively followed from 1994 to 2012, a MPN was present in 28 (23.1%). Additional 13 patients (10.7%) showed only the JAK2 V617F mutation. During the follow-up, the JAK2 V617F mutation and/or MPN were identified in 8 patients (median time of development: 21 months, range 6-120), whereas 72 remained (MPN and JAK2 V617F)-free until the end of the observation. The mortality rate was higher among patients presenting with MPN and/or the JAK2 V617F mutation than in patients who developed later or remained disease-free (p=0.032). The thrombosis-free survival was lower in patients with (p=0.04) or developing later MPN and the JAK2 V617F mutation (p=0.005) than in patients (MPN and JAK2 V617F)-free. The incidence of bleeding was similar among groups.

CONCLUSIONS

MPN with or without circulating positive clones for JAK2 V617F mutation can occur long after a SVT, identifying at risk patients for new thrombotic events. If confirmed in other studies, re-evaluation for JAK2 V617F mutation may be of help in early MPN detection and clinical management of SVT patients.

Cytogenetics, JAK2 and MPL mutations in polycythemia vera, primary myelofibrosis and essential thrombocythemia

Background

The detection of molecular and cytogenetic alterations is important for the diagnosis, prognosis and classification of myeloproliferative neoplasms.

Objectives

The aim of this study was to detect the following mutations: JAK2 V617F, JAK2 exon 12 and MPL W515K/L, besides chromosomal abnormalities. Furthermore, molecular and cytogenetic alterations were correlated with the leukocyte and platelet counts, hemoglobin levels and age in all patients and with the degree of fibrosis in primary myelofibrosis cases.

Methods

Twenty cases of polycythemia vera, 17 of essential thrombocythemia and 21 of primary myelofibrosis were selected in the Hematology Department of the Universidade Federal de São Paulo (UNIFESP) between February 2008 and December 2009. The JAK2 V617F, JAK2 exon 12 mutations, MPL W515K and MPL W515L mutations were investigated by real-time PCR and direct sequencing. G-band karyotyping and fluorescence in situ hybridization were used to detect chromosomal abnormalities.

Results

Chromosomal abnormalities were observed only in polycythemia vera (11.8%) and primary myelofibrosis cases (17.6%), without correlation to clinical data. Chromosomal abnormalities were not detected by fluorescence in situ hybridization. The JAK2 V617F mutation was observed in polycythemia vera (90%), primary myelofibrosis (42.8%) and essential thrombocythemia (47%). Patients with JAK2 V617F-negative polycythemia vera had lower platelet and leukocyte counts compared to V617F-positive polycythemia vera (p-value = 0.0001 and p-value = 0.023, respectively). JAK2 V617F-positive and MPL W515L-positive primary myelofibrosis cases had a higher degree of fibrosis than V617F-negative cases (p-value = 0.022). JAK2 exon 12 mutations were not detected in polycythemia vera patients. The MPL W515L mutation was observed in one case of primary myelofibrosis and in one of essential thrombocythemia. The MPL W515K mutation was not found in patients with essential thrombocythemia or primary myelofibrosis. The MPL W515L-positive patient with primary myelofibrosis had more severe anemia than other patients with primary myelofibrosis.

Conclusions

This study demonstrates that karyotyping for JAK2 and MPL mutations is useful in the diagnosis of myeloproliferative neoplasms. The precise pathogenetic contribution of these alterations is still unclear. However, this study adds more information about the pathophysiology of polycythemia vera, essential thrombocythemia and primary myelofibrosis.

Resveratrol induces cell cycle arrest and apoptosis in malignant NK cells via JAK2/STAT3 pathway inhibition

Natural killer (NK) cell malignancies, particularly aggressive NK cell leukaemias and lymphomas, have poor prognoses. Although recent regimens with L-asparaginase substantially improved outcomes, novel therapeutic approaches are still needed to enhance clinical response. Resveratrol, a naturally occurring polyphenol, has been extensively studied for its anti-inflammatory, cardioprotective and anti-cancer activities. In this study, we investigated the potential anti-tumour activities of resveratrol against the NK cell lines KHYG-1, NKL, NK-92 and NK-YS. Resveratrol induced robust G0/G1 cell cycle arrest, significantly suppressed cell proliferation and induced apoptosis in a dose- and time-dependent manner for all four cell lines. In addition, resveratrol suppressed constitutively active STAT3 in all the cell lines and inhibited JAK2 phosphorylation but had no effect on other upstream mediators of STAT3 activation, such as PTEN, TYK2, and JAK1. Resveratrol also induced downregulation of the anti-apoptotic proteins MCL1 and survivin, two downstream effectors of the STAT3 pathway. Finally, resveratrol induced synergistic effect on the apoptotic and antiproliferative activities of L-asparaginase against KHYG-1, NKL and NK-92 cells. These results suggest that resveratrol may have therapeutic potential against NK cell malignancies. Furthermore, our finding that resveratrol is a bonafide JAK2 inhibitor extends its potential benefits to other diseases with dysregulated JAK2 signaling.

What is the role of JAK2(V617F) mutation in leukemic transformation of myeloproliferative neoplasms?

BACKGROUND AND OBJECTIVES

The role of the Janus kinase 2 V617F (JAK2(V617F)) mutation in the pathogenesis of the various BCR-ABL1-negative myeloproliferative neoplasms (MPNs) remains unclear. Its significance in leukemic transformation is a matter of even greater controversy. The aim of this study was to evaluate both the JAK2(V617F) mutational status of the rare cases in which blast crisis occurred in our institution and the response after intensive treatment.

MATERIALS AND METHODS

Between 1999 and 2009, 778 patients received diagnoses of BCR-ABL1-negative MPNs in our center (395 polycythemia vera, 329 essential thrombocythemia, and 45 primary myelofibrosis cases, as well as 9 MPN cases not otherwise classifiable). Of these patients, 7 developed leukemic transformation. The genotyping of the JAK2(V617F) mutation was performed by the amplification-refractory mutation system.

RESULTS

Six of the 7 patients were tested for JAK2(V617F) in the chronic phase of their disease, and 3 of these patients were positive for JAK2(V617F). These patients, 2 with polycythemia vera and 1 with essential thrombocythemia, also harbored JAK2(V617F) in the heterozygous state during blast crisis and even after intensive treatment in one of these patients. The other cases that evolved to blast crisis did not harbor the JAK2(V617F) mutation before and after transformation. All 7 patients died despite conventional or supportive treatment.

CONCLUSIONS

The transformation of MPNs into acute leukemia is by itself a very rare phenomenon, and so is the persistence of the JAK2(V617F) mutation after blast crisis. In our series, all JAK2(V617F)-positive patients remained positive for this mutation after leukemic transformation, although in the heterozygous state, suggesting that JAK2(V617F) is not essential for transformation in these cases. The fact that all JAK2(V617F)-negative cases remained negative after blast crisis reinforces the theory that other molecular event(s) may play a role in the clonal heterogeneity of MPNs. Owing to the poor outcome of acute myeloid leukemia secondary to MPN, patients should be included in clinical trials of the novel JAK2 inhibitors.